Is that a drain plug in the fuel cap compartment and can it be removed to clean, or is it connected to anything.

There is a drain and it gets easy blocked. Pour lots of hot water to unblock it with soapy water.

It just runs to an outlet to ground in the wheel arch so the best bet is to poke some strimmer wire down it

A second vote for strimmer wire, its very versatile.

It was the only thing strong and bendy enough to clear my rear screen washer feed after the system gunged up 
when two different types of screen wash were mixed.